Wax coatings of improved tack



United States Patent Ofifice 3,365,328 Patented Jan. 23, 1968 ABSTRACT OF THE DISCLOSURE Coated substrates of improved tack time prepared by contacting a substrate with certain molten synthetic waxes of olefins of at least 4 carbon atoms and prior to said contacting incorporating into the synthetic waxes 0.05 to 3% by weight of certain Group I, -II and III metal salts of monoor di-carboxylic or monoor di-sulfonic acids.

This invention relates to hydrocarbon wax coated substrates and their process of preparation. More particularly, this invention relates to substrates coated with a synthetic wax which exhibits a substantially improved tack time in comparison to prior art Waxes. In a specific aspect, this invention relates to substrates coated with butene polymer waxes and a process for preparing the same.

For a number of years, various substrates, including paper, metal foil, fabrics, foodstuffs and the like, have been coated with synthetic waxes prepared from a-monoolefins such as butene to preserve and protect the coated surface. In recent years, melt coating procedures, such as curtain coating have been employed to coat various substrates, particularly those of irregular shape. In this method, the substrate to be coated is passed through a curtain of molten Wax which is provided by a spray head or other suitable means. The wax curtain, except when broken by the passage through it of a substrate, falls directly into a collector and is returned to a molten wax reservoir for reuse. Where a substrate to be coated is regular in shape such as paper, fabric, or the like, the wax is generally applied to the surface to be coated using a gravure roll immersed in a fountain containing the molten wax or it can be applied from a slit die onto the surface and smoothed with a doctor blade. The coated substrate can then be taken up on a rewind roll. Where the substrate has an irregular contour, for example, ham, bacon, nuts, bolts, or the like, it is curtain coated by placing it on a moving belt or roller and passing it rapidly through a curtain of molten wax. The molten wax is cooled substantially simultaneously upon contact with the solid substrate which is usually at a temperature below the melting point of the wax.

The prior art synthetic wax coatings prepared by the above melt coating techniques often exhibit good physical properties, including good clarity and sparkle, tensile strength and toughness. However, these coatings are often tacky for periods of about 120 to about 135 seconds which is a significant disadvantage in commercial coating operations. During the period when the wax coating is tacky, hereinafter referred to as tack time, coated substrates will adhere to one another and to surrounding materials which gives rise to problems in handling these materials and often damages the coating. Furthermore,

substrates such as paper are generally melt coated in commercial operations at high rates, for example, rates of 200 feet per minute and generally rates in excess of 500 feet per minute so that such a prolonged tack time requires slower rates or additional equipment such as conveyors and rollers to run the coating in air until it becomes substantially free of tack. For most melt coating commercial operations tack times no greater than about 45 seconds can be tolerated without any substantial delay in processing.

It is evident, therefore, that the state of the art will be greatly enhanced by providing synthetic wax coatings which have tack times which do not exceed about 45 seconds and often are not in excess of 30 seconds. Likewise, a significant contribution to the art would be substrates coated with such materials and a process for their preparation.

Accordingly, it is an object of this invention to provide synthetic wax coatings exhibiting. improved properties.

Another object of this invention is to provide coated substrates which are coated with a tough synthetic wax which exhibit an improved tack time.

Another object of this invention is to provide synthetic wax coatings which can be applied by melt coating techniques, particularly curtain coating procedures, to substrates without exhibiting the poor tack times characteristic of prior art synthetic wax coatings available heretofore.

Still another object of this invention is to provide a method for obtaining the aforementioned improved synthetic wax coatings and coated substrates.

Other objects and advantages of this invention will become apparent from an examination of the specification and claims that follow.

It has now been found that a particular class of synthetic hydrocarbon waxes, when contacted with a substrate, will form tough coatings having tack times no greater than about 45 seconds if, prior to said contacting, an organic acid salt, as hereinafter described, is incorporated into the wax.

The fact that the organic acid salts can be incorporated into the synthetic hydrocarbon waxes, as hereinafter described, to form tough coatings exhibiting improved tack times was completely unexpected. Thus, organic acid salts have been added to hydrocarbon wax polymers such as polyethylene and polypropylene to nucleate the polymer which increases the rate of crystallization. This general- 1y results in a coating which is hard, but very brittle. It would have been expected, therefore, that the method described herein would give hard, brittle coatings rather than tough coatings having improved tack times.

The organic acid salts employed in the practice of this invention include the known Group I, II and III metal salts of monoor dicarboxylic or mono or disulfonic acids. The organic acid salts generally contain 224 carbon atoms, although very good results are obtained with those containing 6-16 or even 6-12 carbon atoms. These organic acid salts can be defined by formulae:

and

Where n=1, R is a monovalent hydrocarbyl radical containing up to 2 hydroxy groups and up to 24 carbon atoms, where n:2, R is a divalent hydrocarbyl radical containing up to 20 carbon atoms and M is a metal selected from the group consisting of Group I-A, II and IIIA of the Periodic Table.

As already indicated, where ":1, R in the above formulae can be any monovalent hydrocarbyl radical such as alkyl, aryl, aralkyl or alicyclic radical containing up to 24, preferably 6-16 carbon atoms. Examples of such radicals include methyl, ethyl, propyl, butyl, decyl, d0- decyl, tetratlecyl, toluyl, naphthyl, benzyl, cyclobutyl, cyclohexyl, cyclopentyl and the like. Generally the radicals are hydrocarbon but they can contain no more than 2 hydroxy groups such as, in the case of aluminum dihydroxystearate. Other substituents which are not hydrocarbon, e.g,. alkoxy, aryloxy or acyl, can be present in the R radical, but only if the particular substituent does not deleteriously affect the desired result of decreasing tack time. In fact, some of the non-hydrocarbon groups can be present as substituents on the metal if the di or trivalent metal salts are employed, as long as these substituents do not deleteriously affect the action of the salt in reducing tack time. Where n=2, R can be any divalent hydrocarbyl radical containing up to 20, and preferably, 616, carbon atoms. Such radicals include the alkylene, arylene, aralkylene, or divalent alicyciic radicals, as exemplified by methylene, ethylene, propylene, phenylene, naphthylene, cyclopentylene, cyclohexylene and the like.

The metals employed to form the organic acid salts employed in the practice of this invention are Group I-A, II or III-A metals of the Periodic Table. Included in this group of metals are, for example, lithium, sodium, potassium, magnesium, calcium, barium, zinc, cadmium, mercury, aluminum, gallium and the like. A copy of the Periodic Table referred to herein can be found in Langes Handbook of Chemistry, 9th edition, published by Handbook Publishers, Inc. at pages 56 and 57, for example.

Suitable organic acid salts which can be used in the method of this invention are exemplified by lithium benzilate, potassium phenylacetate, lithium l-naphthoate, zinc S-hydroxy-l-naphthoate, sodium palmitate, magnesium naphthalate, sodium benzenesulfonate, zinc p-phenolsulfonate, sodium 3methyl-l-butanesulfonate, potassium 2,4-dimethylbenzenesulfonate, magnesium 2,5-dimethylbenzenesulfonate, lithium hexanoate, lithium hydroxystearate, sodium stearate, magnesium hydroxystearate, aluminum dihydroxystearate, potassium myristate, zinc 2-ethylhexanoate, calcium decanoate, sodium eicosoate, lithium adipate, sodium sebacate, potassium dodecanedioate, magnesium terephthalate, lithium, 1,4-cyclohexanedicarboxylate, disodium 1,S-naphthalenedisulfonate, calcium p-toluenesulfonate, potassium l-anthroate, lithium 4-(l-methylheptadecyl)-benzenesulfonate, and the like.

It has been found that synthetic hydrocarbon waxes, if they have the properties set forth hereinafter, can be employed in the method of this invention to form coatings that are tack free in 45 seconds, generally 30 seconds or less, and exhibit other good physical properties, including good toughness. The polymers employed are low molecular weight hydrocarbon polymers of ot-olefins containing at least 4 carbon atoms. These polymers have a density in a range of about 0.83 to about 0.94, preferably, about 0.88 to about 0.93, an inherent viscosity in the range of about 0.2 to about 0.5, preferably about 0.25 to about 0.4, in tetralin at 145 C. and a melt viscosity in the range of about 1,500 to about 20,000 cp., preferably about 5,000 to about 10,000 cp. at 190 C. These waxes generally melt below about 180 C. and have brittle points no lower than C., preferably in the range of about 10 to about 60 C.

Although any of the aforementioned synthetic hydrocarbon Waxes can be employed in the process of the invention, it is preferred that the waxes be low molecular Weight homo or copolymers of the well-known polymerizable aliphatic a-monoolefins containing 4-10 carbon atoms. The copolymer waxes employed in practicing this invention can be random or block copolymers as long as they have the properties described hereinabove. When copolymers of the vt-olefins are employed in the process of this invention, it is generally most desirable to use copolymers containing at least 40%, and more preferably, about 40-45%, by weight, of one of the aliphatic aolefins containing 46 atoms, preferably l-butene. The copolymers of a-olefins containing at least 4 carbon atoms with lower aliphatic a-olefins such as ethylene or propylene, should usually contain no more than about 60%, preferably no more than about 40 to 50%, by weight, of the ethylene or propylene for best results in the practice of this invention. The Ot-OlCfiIlS that are most often used to form the hydrocarbon waxes employed in the process of this invention will generally have the formula CHF-CHR Where R is an alkyl radical containing at least 2 carbon atoms. Examples of such a-olefins include l-butene, 4- methyl-l-pentene, 4-methyl-1-hexene, S-methyl-l-hexene, 4,4-dimethyl-l-pentene, 3-methyl-l-butene, l-pentene, 1- hexenc, l-octene, l decene, and the like.

The various properties of the synthetic hydrocarbon waxes referred to hereinbefore can be determined using any of the procedures generally employed for this purpose. For example, the melt viscosity can be determined using a standard Brookfield viscometer or a Capillary Melt Method. The inherent viscosity of the hydrocarbon wax employed can be determined in tetralin at C., a typical procedure being described by Schulken et al. in The Journal of Polymer Science, volume 26, page 227 (1957), and the brittle point can be determined using the procedure described in ASTM D746-57T employing a sample which is in the order of 5 to 10 mils in thickness. The melting point of the wax can be determined by any suitable method generally employed for this purpose. One such method is the D.T.A. (Differential Thermal Analysis) method which has been used extensively to determine polymer melting points and is described in Organic Analysis, vol. 4, Interscience Publishing Co. (1960), page 361.

As already indicated, a suitable tack time for most commercial melt coating applications is no greater than about 45 seconds, preferably below 30 seconds. Tack time, as discussed herein, can be defined as that period when a synthetic wax coating is tacky or sticky to the touch and tends to adhere to other materials. A simple test for establishing the tack time of a wax coating is merely to touch the coating with the finger. If the coating tends to adhere to the finger upon touching after a period of 45 seconds, it is not suitable for most commercial operations.

In practicing this invention, the hydrocarbon waxes in the molten state are generally contacted with the substrate to be coated at temperatures up to about C. Coating temperatures in the range of about 0 to about 180 C. can be employed, although it is desirable to operate at temperatures of about 20 C. It should be understood, however, that good results can be achieved by varying the coating temperature to suit the nature and composition of the particular hydrocarbon wax employed.

Temperatures substantially in excess of about 180 C. are generally not satisfactory because the prolonged heating employed in melt-coating operations can cause excessive oxidation of the synthetic wax which deleteriously affects the coating. Furthermore, if the substrate to be coated is bacon or some other foodstuff, temperatures above about 180 C. often result in cooking the material which obviously should be avoided.

Any of the conventional methods of melt coating can be employed in practicing this invention. For example, the hydrocarbon wax can be applied to the substrate using a gravure roll} immersed in a fountain containing the molten wax or it can be applied from a slit die onto the surface of the substrate and smoothed with a doctor blade. The wax coating can also be applied using the curtain coating technique which is particularly advantageous where the substrate to be coated is of irregular form. In general, the coating formed should have a thickness no greater than about 60 mils, preferably about 1 to about mils.

A wax coating prepared according to the process of this invention using the curtain coating method adheres to an object and follows the contour of irregularly shaped articles to form clear coatings with improved tack times. Furthermore, if articles to be coated are placed upon a support and both support and article are passed through a curtain of molten wax, there results an attractive package in which the wax coating adheres to the article and secures it to the support. Such coatings do not bridge or balloon from the article to the support, but rather, follow the contour of the article and support. Using this method, it is possible, therefore, to package such irregularly shaped articles as nuts, bolts, screw drivers, ham slices and bacon slices in an attractive manner.

The organic acid salts give good results when used in concentrations of at least 0.05%, generally about 0.05 to about 3%, and preferably 0.5 to about 1.5%, by weight, based on the synthetic wax. The salt can be added to the synthetic wax while in the molten state or it can be incorporated prior to melting the wax. Any desired blending method can be employed, e.g., mechanical mixing or other blending method as long as the organic acid salt is uniformly distributed throughout the synthetic wax.

In general, the process of this invention can be used to coat any substrate and the coating can be applied to one or more sides of the substrate. In addition to coating paper for packaging as above described, this invention can be used to coat any surface, including substrates such as foil, glass, fabric, wood, ham, bacon, bologna, nuts, bolts, screw drivers, pliers and the like.

This invention can be further illustrated by the following examples of preferred embodiments thereof although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

Example 1 The molten synthetic hydrocarbon waxes of polymers of a-olefins containing at least 4 carbon atoms generally form coatings having tack times in excess of 100 seconds. To illustrate, 50 lbs. of a 1-butene propylene copolymer wax containing approximately 60%, by weight, l-butene is melt cast into a 5 mil film using a hot doctor blade. The polymer wax has a density of 0.88, an inherent viscosity in tetralin at 145 C. of 0.42 and a melt viscosity of 8,000 cp. at 190 C. The coating is quenched while still molten with water at 25 C. for seconds. The resulting film is tough but shows a tack time of 135 seconds.

Example 2 The incorporation of the organic acid salts described hereinbefore, prior to contact with asubstrate, substantially reduces tack time without deleteriously affecting other properties of a synthetic wax. To illustrate, the propylene l-butene copolymer wax of Example 1 is compounded with each of the metal salts listed in Table 1 below. Good dispersions are obtained by ball milling the salts before blending them with the molten wax. The tack time of each wax sample is determined using a water quenched sample as in Example 1.

It can be seen from a comparison of the results set forth in the above table with those obtained in Example 1, that the method of this invention gives a significant improvement in tack time.

Similar results are obtained with polybutene wax having a density of 0.90, an inherent viscosity in tetralin at 145 C. of 0.31 and a melt viscosity of 5,500 cp. at 190 C.

Example 3 A hydrocarbon copolymer wax of wt. percent propylene and 50 wt. percent l-hexene, having a density of 0.87, an inherent viscosity of 6,500 cp. at 190, has a tack time of 195 seconds after water quenching according to Example 1. This Wax is blended with each of the agents listed in Table 2 below. The tack time of each composition is measured after water quenching, as described in Example 1.

TABLE 2 Coneen- Tack Agent tration, Time,

Weight Seconds Percent Lithium hexanoate 0. 7 44 Zinc lethylhexanoate O. 9 41 Calcium deeanoate. 1. 5 38 Sodium eicosoatenn 3.0 32 Sodium sebaeate. 1. 0 34 Magnesium terephthalate 0. 5 45 Lithium benzi1ate 0. 5 35 Aluminum suceinate 0. 5 25 Sodium 3-methyl-l-butanesulfonate 0. 5 29 Potassium 2,4-dimethyl-benzene-sulfonate. 0.7 29 Disodium 1,fi-naphthalene-disulfonate 0. 3 45 Substantially the same results are obtained with a l-butene l-hexene copolymer wax having a density of 0.90 and a melt viscosity of 16,000 cp. at C.

Example 4 A copolymer wax of 45%, by weight, l-octene and 55%, by weight, propylene, having a melt viscosity of 10,000 cp. at 190 C. gives a water quenched film having 7 a tack time of 63 seconds. This wax is compounded with each of the agents listed in Table 3 using the procedure of Example 2.

Similar results are obtained when poly-l-pentene, polyl-hexene and poly-l-decene having approximately the same density, inherent viscosity and melt viscosity are substituted for the l-octene propylene copolymer Wax in the above procedure.

Example 5 As previously indicated, wax coatings of polymers of a-olefins containing less than 4 carbon atoms will not exhibit improved tack times and toughness in the process of this invention. To illustrate, the procedure of Example 2 is repeated using polypropylene wax having a density of 0.91, an inherent viscosity of 0.5 in tetralin at 145 C. and a melt viscosity of 20,000 cp. at 190 C. No improvement in tack time for the polypropylene wax coating is observed over coatings formed from the same wax containing no organic acid salt.

Thus, by means of this invention there is provided novel hydrocarbon wax coatings exhibiting excellent physical properties including a substantially reduced tack time in comparison to hydrocarbon wax coatings now available. Substrates coated according to the process of this invention can be used in packaging food, dry goods and other articles which require protection from moisture or air.

Although the invention has been described in considerable detail with reference 'to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. The method which comprises contacting a molten synthetic Wax of a hydrocanbon polymer of an a-olefin containing at least 4 carbon atoms having a density in the range of about 0.83 to about 0.94, an inherent viscosity in tetralin at 145 C. in the range of about 0.2 to about 0.5 and a melt viscosity at 190 C. in the range of about 1,500 to about 20,000 cp. with a substrate and, prior to said contacting, incorporating into said synthetic wax, about 0.05 to about 3%, by weight, of a salt having a formula selected from the group consisting of:

where n is an integer from 1 to 2, v is an integer from 1 to 3, X is an integer from 1 to 3, y is an integer from 1 to 2 and equal to where 11:1, R is a monovalent hydrocarbyl radical containing up to 2 hydroxy groups and up to 24 carbon atoms, where 12:2, R is a divalent hydrocarbyl radical containing up to 20 carbon atoms and M is a metal selected from the metals in Group LA, 11 and Ill-A of the Periodic Table, said synthetic wax composition having a tack time not in excess of 45 seconds.

2. The method of claim 1 in which the salt incorporated into the synthetic wax has Formula 1.

3. The method of claim 1 in which the salt incorporated into the synthetic Wax has Formula 2.

4. The method of claim 1 in which about 0.5 to about 1.5%, by weight, of the salt is incorporated into the wax.

5. The method which comprises contacting a molten synthetic Wax of a hydrocarbon polymer of an a-olefin containing at least 4 carbon atoms having a density in the range of about 0.88 to about 0.93, an inherent viscosity in tetralin at C. in the range of about 0.25 to about 0.4 and a melt viscosity at C. in the range of about 5,000 to about 10,000, with a substrate and, prior to said contacting, incorporating into said synthetic wax, about 0.5 to about 1.5%, by weight, of a salt having a formula selected from the group consisting of:

tty

o t o II and where 11:1, R is a monovalent hydrocarbyl radical containing up to 2 hydroxy groups and up to 24 carbon atoms, where 11:2, R is a divalent hydrocarbyl radical containing up to 20 carbon atoms and M is a metal selected from the metals in Group I-A, II and IIIA of the Periodic Table, said synthetic wax composition having a tack time not in excess of 45 seconds.

6. The method of claim 5 in which the synthetic wax is a l-butene-propylene copolymer containing about 40% to about 45%, by weight, of l-butene.

7. The method which comprises contacting a molten synthetic wax of a l-butene propylene copolymer containing about 60%, by Weight, of l-butene having a density of about 0.88, an inherent viscosity in tetralin at 145 C. of about 0.42 and a melt viscosity of about 8,000 cp. at 190 C. with a substrate and, prior to said contacting, incorporating into said synthetic wax, about 0.5%, by weight, of lithium hydroxy stearate, said synthetic wax composition having a tack time not in excess of 45 seconds.

8. The method which comprises contacting a molten synthetic Wax of a l-butene propylene copolymer containing about 60%, by weight, of l-butene, having a density of about 0.88, an inherent viscosity in tetralin at 145 C. of about 0.42 and a melt viscosity of about 8,000 cp. at 190 C. with a substrate and, prior to said contacting, incorporating into said synthetic wax, about 0.5%, by weight, of sodium stearate, said synthetic wax composition having a tack time not in excess of 45 seconds.

9. The method which comprises contacting a molten synthetic wax of a l-butene propylene copolymer containing about 60%, by weight, of l-butene, having a density of about 0.88, an inherent viscosity in tetralin at 145 C. of about 0.42 and a melt viscosity of about 8,000 cp. at 190 C. with a substrate and, prior to said contacting, incorporating into said synthetic wax about 0.7%, by weight, of magnesium hydroxystearate, said synthetic wax composition having a tack time not in excess of 45 seconds.

10. The method which comprises contacting a molten synthetic wax of a l-butene propylene copolymer containing about 60%, by weight, of l-butene having a density of about 0.88, an inherent viscosity in tetralin at 145 C. of about 0.42 and a melt viscosity of about 8,000 cp'. at 190 C. with a substrate and, prior to said contacting, incorporating into said synthetic wax about 0.9%, by weight, of calcium p-toluenesulfonate, said synthetic wax composition having a tack time not in excess of 45 seconds.

11. The method which comprises contacting a molten synthetic wax of a l-butene propylene copolymer containing about 60%, by weight, of l-butene having a density of about 0.88, an inherent viscosity in tetralin at 145 C. of about 0.42 and a melt viscosity of about 8,000 cp at 190 C. with a substrate and, prior to said contacting, incorporating into said synthetic wax about 0.1%, by weight, of sodium benzenesulfonate, said synthetic wax 10 com-position having a tack time not in excess of 45 seconds.

12. The product obtained by the process of claim 1.

References Cited UNITED STATES PATENTS 2,348,687 5/1944 Abrams et al. 106219 2,402,903 6/1946 Massey et al 117168 2,405,977 8/ 1946 Peters 264216 2,477,619 6/1949 Farrell et al. 161160 2,728,684 12/19'55 Darragh 106285 2,728,735 12/1955 Anderson 260-285 3,080,330 3/1963 Rudel et a1 260-l8 3,118,847 1/1964 Greear et al 260-23 WILLIAM D. MARTIN, Primary Examiner.

W. D. HERRICK, Assistant Examiner. 

